The invention relates to an appliance for the spray coating of workpieces with paint, which has at least two coating booths, arrange on a conveying track for the workpieces, and a spray device. Such a spray-coating appliance is suitable particularly for electrostatic powder coating.
The principle of electrostatic powder coating is employed primarily for the lacquering of sheet-metal and finished parts, since it is particularly economical and environmentally friendly. Furthermore, high throughput quantities of material to be lacquered can be achieved with powder-coating systems.
In conventional powder-coating systems, however, as in lacquering systems working according to other paint-coating methods, problems arise when the colour is changed. In particular, in order to achieve a homogeneous and uniform coating along with a high throughput of material to be lacquered, a concentrated paint-powder jet is directed onto the workpiece to be lacquered, but only some of the paint powder adheres to the workpiece, whereas the remaining paint powder settles in the system.
The known coating systems therefore have a suction-extraction device., in order to return the paint-powder excess into the paint-powder circuit. However, paint-powder particles always remain adhering particularly to the coating-booth walls and, in the event of a change of colour, cause colour mixing and consequently an impurity. In order to avoid this, the coating booth has to be cleaned whenever the colour is changed. This therefore always gives rise to costly standstill times in the coating system.
Moreover, particularly in an electrostatic powder-coating system, a relatively great amount of time is needed for cleaning during a colour change, since the paint-powder particles, by virtue of their electrical charge, often adhere firmly to the coating booths.
In order to allow a rapid colour change in powder-coating systems, powder-coating systems possessing a plurality of coating booths for different colours, so that one booth can always be cleaned alternately for the colour change, are already being used. CH 668 008 A5 describes such a powder-coating system having two coating booths which are arranged parallel to one another and are supplied by means of a switch via a common conveying track. However, this system is very costly, since two complete coating booths, each provided with a spray device, are necessary.